Coop Walls in the NorthEast

So I am constructing my first coop (will provide pictures soon) and am getting ready to put the walls on. Is having the wall made out of T1-11 siding sufficient, or should that go on top of a plywood (OSB) sub layer for additional insulation?

You do not need the insulation, but you might do it if you think it keeps the coop less drafty. Chickens can tolerate very cold temperatures with ease (if they have large combs, the combs can get frost bitten, but otherwise cold is not an issue) What chickens need is a protected area where they will not get wet and do not have too strong of a breeze aimed directly at where they roost.
They do need good ventilation, ideally above where the chickens roost, to keep the coop from becoming too humid (again very important to stay dry)

My coop is in Montana. The girls did fine while living in an uninsulated coop with the upper vents open year round. I have the roosts down low so that no breeze from the upper vents blows on the birds. The roosts are made from 2 x 4s with the wide side up so the birds can sit on their own feet and keep them warm when they roost. The temps went down to -12.

Dry birds are warm birds. Birds make a lot of moisture with breathing and pooing. To keep them warm you need to get that moisture out of the coop. The warm moist air naturally rises and leaves the coop through the high vents, thereby keeping the birds warm. Remember, the birds are covered in nice warm down. My lightweight down comforter keeps me warm just as the birds' down keeps them warm. I also keep the water outside in the run so that won't add to the moisture in the coop.